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BERS Methodology

The aim of this supplementary document is to provide the supporting survey methodology, relevant legislation and bibliography used for the creation of the main Bat Emergence and Re-entry Surveys (BERS) report.

The intention is to enable the main report to be as easy as possible to read, to help with understanding the conclusions, impacts, and recommendations made.

Scope of the Report

The report provides a description of the bat activity observed and recorded during BERS. The aim of the surveys is to determine the presence or likely absence of bats, and/or to characterise any roosts present including species, number of individuals, number and location of roost access points, and to gain an understanding of how bats use the site. The report provides information on possible constraints to the proposed development as a result of bats and summarises the requirements for any mitigation proposals, including a European Protected Species Licence (EPSL), where appropriate, to achieve planning or other statutory consent and to comply with wildlife legislation.

To achieve this, the following steps have been taken:

  • BERS of built structures and/or trees has been undertaken to determine the presence or likely absence of bat roosts.
  • An outline of potential impacts on any confirmed or unidentified roosts has been provided, based on the proposed development.
  • Recommendations for mitigation have been made, along with advice on the requirements for a European Protected Species Licence (EPSL) application if appropriate.
  • Opportunities for the enhancement of the site for roosting, foraging and commuting bats have been set out.

Survey Methodology

The number of evening emergence surveys has been calculated for each BERS survey based on Table 7.1 of the 4th edition Bat Surveys for Professional Ecologists —Good Practice Guidelines (Collins, J, 2023). Recommendations for further surveys and mitigation have been made based on the above points and based on tables 7.1 and 7.2 of the bat survey guidance.

A survey plan and location map are presented in the report, along with a plan of the proposed development (where available and relevant).

Dusk emergence surveys commence 15 minutes before sunset and continue for 1½ – 2 hours after sunset – depending upon bat activity, the nature of the suspected roost involved and surveyor visibility. Surveys continue for the full 2 hours where the presence of roosts of late emerging species (such as Brown Long-eared bats) are suspected.

Surveys were completed during optimal weather conditions i.e., when temperatures were above 10 C, with no rain or strong winds (greater than 5m/s), as these adverse weather conditions can impact upon bat emergence and foraging behaviour. Periods of high moon illuminance (>80%) were also avoided insofar as possible as this can reduce bat activity.

Where multiple surveys are conducted, these surveys are a minimum of three weeks apart.

The survey(s) involve surveyors positioned around each relevant building/tree, ensuring that all elevations and roof sections/sides of the tree with suitable roosting features could be clearly observed by a surveyor and/or infrared camera. Particular attention was paid to the areas of the building/tree identified as providing suitable access points to bat roosts. Each surveyor and camera was assigned an area of the building/tree to observe for the duration of the survey.

Surveyors use heterodyne and frequency division bat detectors, and Echo Meter Touch detectors connected to iPads or Android tablets. Bat echolocation calls recorded during the surveys are analysed using Wildlife Acoustics sound analysis software Kaleidoscope V3.1.7 when required. The Echo Meter Touch includes an auto ID function for bat species; however, this is not 100% accurate and further post-survey sound analysis is often required to confirm species that could not be identified by the auto ID software during the survey.

Surveyors also use head torches (red light only), survey record sheets and pens/pencils for recording all activity observed during the surveys. Each surveyor is also provided with a handheld radio for communication between surveyors to assist with confirming ambiguous bat activity e.g. a bat emergence or a bat passing over the building/tree.

Survey Methodology – Night Vision Aids

In line with the 4th edition guidelines, a night vision aid (NVA) was set up to monitor each survey position building/tree during the BERS. For the majority of Arbtech sites, this comprises an infrared camera (a Nightfox Whisker) set up on a tripod with one separate Nightfox XB5 pro torch (or equivalent illumination source) on a second tripod to provide additional illumination. Analysis of the footage was subsequently undertaken to detect roosting activity. In some cases, equipment may differ (for example the use of Canon XA cameras rather than Nightfox Whiskers) and if this occurs it will be stated in the relevant report.

Cameras are typically deployed alongside surveyors to maximise the efficacy of both in detecting bats. Occasionally, unmanned NVAs will be deployed, in line with the advice in the 4th edition guidelines that “when used appropriately, NVAs can be used to reduce the number of surveyors” (Collins, J, 2023; 7.2.11, p69). Unmanned cameras are deployed where they can be visually supervised by a human surveyor, and they are accompanied by an accompanying bat detector which is capable of recording. Any footage from these unmanned NVAs is subjected to additional manual review. A maximum ratio of 2 cameras to every one human surveyor is utilised on sites.

Analysis of footage collected by these NVAs follows one of two methodologies:

Partial Hybrid Review (manned cameras only): As the camera is accompanied by a human surveyor who is visually surveying the building/tree during the survey, it is not considered necessary to review the full 2 hours of footage collected by each camera. Instead, the reviewer manually reviews 1-5 minute segments which may contain bat activity or other relevant motion as identified by the original surveyor on their survey sheet. This review is conducted using appropriate video analysis software (VLCmedia player or equivalent) at between 1x and 1.5x speed. To add robustness to this process, after the human review an AI motion analysis program such as Motionmeerkat, Batscan or equivalent is utilised to quality control this review. This software flags up motion in the video and provides additional individual frames and/or clips of motion to be manually reviewed by the human reviewer.

Full Review (unmanned cameras): The full video, including an audio track from an accompanying bat detector, is reviewed manually by a human surveyor using appropriate video analysis software (VLCmedia player or equivalent) at between 1x and 1.5x speed. Any emergences or other relevant bat activity are noted. At the end of this process, an AI motion analysis program such as Motionmeerkat, Batscan or equivalent is utilised for quality control. This software flags up motion in the video, providing individual frames and/or clips of motion to be reviewed to prevent false negatives.

Occasional spot-checks (full manual reviews) are performed upon a proportion of the videos collected during the season, to ensure the efficacy of these review processes. Internal data on the efficacy and reliability of this methodology will be provided when this process has provided enough data for statistical robustness.  


Bat Tree Habitat Key. (2018). Bat Roosts in Trees: A Guide to Identification and Assessment for Tree-Care and Ecology Professionals. Pelagic Publishing Ltd. Chartered Institute of Ecology and Environmental Management (2020). Guidelines for Accessing, Using and Sharing Biodiversity Data in the UK. 2nd Edition. Chartered Institute of Ecology and Environmental Management, Winchester.

Chartered Institute of Ecology and Environmental Management (2017). Guidelines on Ecological Report Writing. Chartered Institute of Ecology and Environmental Management, Winchester.

Collins, J. (2023). Bat Surveys for Professional Ecologists —Good Practice Guidelines, 4th edition, Bat Conservation Trust, London.

Garland, L. & Markham, S. (2008) Is Important Bat Foraging and Commuting Habitat Legally Protected? http://biodiversitybydesign.co.uk/cmsAdmin/uploads/protection-for-bat-habitat-sep-2007.pdf

Institution of Lighting Professionals (2023). Guidance Note GN08/23 Bats and Artificial Lighting at Night. Bats and the Built Environment Series Publication.

JNCC (2004). Bat Workers Manual, 3rd Edition. http://jncc.detra.gov.uk/page-2861

Magic Database. http://www.magic.gov.uk/MagicMap.aspx

Reason, P.F. and Wray, S. (2023). UK Bat Mitigation Guidelines: a guide to impact assessment, mitigation and compensation for developments affecting bats. Chartered Institute of Ecology and Environmental Management, Ampfield

Natural England Designated Sites View. https://designatedsites.naturalengland.org.uk/SiteSearch.aspx

National Planning Policy Framework (2023). https://www.gov.uk/government/publications/national-planning-policy-framework

Wray, S., Wells, D., Long, E., Mitchell-Jones, T (2010) Valuing Bats in Ecological Impact Assessment. IEEM In-Practice. Number 70 (December 2010). Pp. 23-25.

Relevant Legislation and Planning Policy

National and European Legislation Afforded to Species

The Conservation of Habitats and Species Regulations 2017 (as amended)

The Conservation of Habitats and Species Regulations 2017 (as amended) aims to promote the maintenance of biodiversity by requiring the Secretary of State to take measures to maintain or restore wild species listed within the Regulations at a favourable conservation status.

The Regulations make it an offence (subject to exceptions) to deliberately capture, kill, disturb, or trade in the animals listed in Schedule 2.

However, these actions can be made lawful through the granting of licenses by the appropriate authorities. Licenses may be granted for a number of purposes (such as science and education, conservation, preserving public health and safety), but only after the appropriate authority is satisfied that there are no satisfactory alternatives and that such actions will have no detrimental effect on wild population of the species concerned.

The Wildlife and Countryside Act (WCA) 1981 (as amended)

The Wildlife and Countryside Act (WCA) 1981 (as amended) implements the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention 1979, implemented 1982) and implements the species protection requirements of EC Birds Directive 2009/147 /EC on the conservation of wild birds in Great Britain (the birds Directive). The WCA 1981 has been subject to a number of amendments, the most important of which are through the Countryside and Rights of Way (CRoW) Act (2000).

Other legislative Acts affording protection to wildlife and their habitats include:

Natural Environment & Rural Communities (NERC) Act 2006

Wild Mammals (Protection) Act 1996


All species are fully protected by Habitats Regulations 2010 as they are listed on Schedule 2. Regulation 41 prohibits:

  • Deliberate killing, injuring or capturing of Schedule 2 species (e.g. All bats)
  • Harass a bat or a group of bats (Scotland)
  • Deliberate disturbance of bat species in such a way as:
  • To impair their ability to survive, breed, or reproduce, or to rear or nurture young;
  • To impair their ability to hibernate or migrate
  • To affect significantly the local distribution or abundance of the species
  • Damage or destruction of a breeding site or resting place – even if bats are not occupying it at the time.
  • Bats are afforded the following additional protection through the WCA as they are included on Schedule 5:
  • Intentional or reckless disturbance (at any level)
  • Intentional or reckless obstruction of access to any place of shelter or protection
  • Possess or advertise/see/exchange a bat of a species found in the wild in the EU (dead or alive) or any part of a bat

Effects on development works:

A European Protected Species Licence (EPSL) issued by the relevant countryside agency (i.e. Natural England, Natural Resources Wales, Scottish Natural Heritage) will be required for works are likely to affect a bat roost or an operation which are likely to result in an illegal level of disturbance to the species will require an EPSM licence. The licence is to allow derogation from the legislation through the application of appropriate mitigation measures and monitoring.


National Planning Policy Framework 2021

The National Planning Policy Framework promotes sustainable development. The Framework specifies the need for protection of designated sites and priority habitats and species. An emphasis is also made on the need for ecological infrastructure through protection, restoration and re-creation. The protection and recovery of priority species (considered likely to be those listed as species of principal importance under Section 41 of the Natural Environment and Rural Communities (NERC) Act 2006) is also listed as a requirement of planning policy.

In determining a planning application, planning authorities should aim to conserve and enhance biodiversity by ensuring that: designated sites are protected from harm; there is appropriate mitigation or compensation where significant harm cannot be avoided; measurable gains in biodiversity in and around developments are incorporated; and planning permission is refused for development resulting in the loss or deterioration of irreplaceable habitats including aged or veteran trees and also ancient woodland.

The Natural Environment and Rural Communities Act 2006 and the Biodiversity Duty

Section 40 of the Natural Environment and Rural Communities (NERC) Act 2006, requires all public bodies to have regard to biodiversity conservation when carrying out their functions. This is commonly referred to as the ‘biodiversity duty’.

Section 41 of the Act requires the Secretary of State to publish a list of habitats and species which are of ‘principal importance for the conservation of biodiversity’. This list is intended to assist decision makers such as public bodies in implementing their duty under Section 40 of the Act. Under the Act these habitats and species are regarded as a material consideration in determining planning applications. A developer must show that their protection has been adequately addressed within a development proposal.

European Protected Species Policies

In December 2016 Natural England officially introduced the four licensing policies throughout England. The four policies seek to achieve better outcomes for European Protected Species (EPS) and reduce unnecessary costs, delays and uncertainty that can be inherent in the current standard EPS licensing system. The policies are summarised as follows:

Policy 1; provides greater flexibility in exclusion and relocation activities, where there is investment in habitat provision;

Policy 2; provides greater flexibility in the location of compensatory habitat;

Policy 3; provides greater flexibility on exclusion measures where this will allow EPS to use temporary habitat; and,

Policy 4; provides a reduced survey effort in circumstances where the impacts of development can be confidently predicted.

The four policies have been designed to have a net benefit for EPS by improving populations overall and not just protecting individuals within development sites. Most notably Natural England now recognises that the Habitats Regulations legal framework now applies to ‘local populations’ of EPS and not individuals/site populations.

Limitations and Copyright

Arbtech Consulting Limited has prepared this report for the sole use of the above-named client or their agents in accordance with our General Terms and Conditions, under which our services are performed. It is expressly stated that no other warranty, expressed or implied, is made as to the professional advice included in this report or any other services provided by us. This report may not be relied upon by any other party without the prior and express written agreement of Arbtech Consulting Limited. The assessments made assume that the sites and facilities will continue to be used for their current purpose without significant change. The conclusions and recommendations contained in this report are based upon information provided by third parties. Information obtained from third parties has not been independently verified by Arbtech Consulting Limited.

© This report is the copyright of Arbtech Consulting Limited. Any unauthorised reproduction or usage by any person other than the addressee is strictly prohibited.


This assessment has been designed to meet:

Collins, J. (2023). Bat Surveys for Professional Ecologists —Good Practice Guidelines, 4th edition, Bat Conservation Trust, London; and
British Standard 42020 (2013) ‘Biodiversity – Code of Practice for Planning and Development’.


The work involved in preparing and implementing all ecological surveys, impact assessments and measures for avoidance, mitigation, compensation and enhancement should be proportionate to the predicted degree of risk to bats and to the nature and scale of the proposed development. Consequently, the decision-maker should only request supporting information and conservation measures that are relevant, necessary and material to the application in question. Similarly, the decision-maker and their consultees should ensure that any comments and advice made over an application are also proportionate.

This approach is enshrined in Government planning guidance, for example, the National Planning Policy Framework for England 2023. The desk studies and field surveys undertaken to provide a Preliminary Roost Assessment (PRA) might in some cases be all that is necessary. (BS 42020, 2013)

In consequence of the scale and intensity of the proposed development, showing no impacts on any bats, roost or roost features identified through both the site survey and search of local biological records, and the passive-interface with the mitigation hierarchy, this plan-led report is considered adequate and proportionate. It communicates all relevant information necessary to determine a planning application or support the recommendations for further surveys.

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